The overflow rate of poppet relief valve is established, and the dynamics characteristics of poppet relief valve which contains transient flow force and steady flow force are established. Based on this point, the stability conditions of poppet relief valve system was derived using RouthHurmitz method. The correctness was verified through comparative study in experiment. The effect of the design parameters of relief valve on the dynamic characteristics of poppet valve system was analyzed. Using sensitivity analysis the effects of parameters of the most significant was obtained, that is Liquid flow control body diameter D. The results show that, the established model can largely capture the real dynamic characteristics of the relief valve system, and the established stability condition can be used as a favorable basis for the design of valve.